Laravel 5.6: Unsupported operand types

Question

I am on Laravel 5.6 with PHP 7.3. Whenever I try to login to my app it throws the following error:

Unsupported operand types {"exception":"[object] (Symfony\Component\Debug\Exception\FatalThrowableError(code: 0): Unsupported operand types at /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Support/Arr.php:219) [stacktrace]

Here is the stack trace:

[2020-11-03 06:26:10] local.ERROR: Unsupported operand types {"exception":"[object] (Symfony\\Component\\Debug\\Exception\\FatalThrowableError(code: 0): Unsupported operand types at /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Support/Arr.php:219)
[stacktrace]
#0 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php(2642): Illuminate\\Support\\Arr::flatten(Array)
#1 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php(1963): Illuminate\\Database\\Query\\Builder->getBindings()
#2 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php(1951): Illuminate\\Database\\Query\\Builder->runSelect()
#3 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php(2435): Illuminate\\Database\\Query\\Builder->Illuminate\\Database\\Query\\{closure}()
#4 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php(1952): Illuminate\\Database\\Query\\Builder->onceWithColumns(Array, Object(Closure))
#5 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php(2362): Illuminate\\Database\\Query\\Builder->get(Array)
#6 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Database/Query/Builder.php(2290): Illuminate\\Database\\Query\\Builder->aggregate('count', Array)
#7 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Validation/DatabasePresenceVerifier.php(55): Illuminate\\Database\\Query\\Builder->count()
#8 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Validation/Concerns/ValidatesAttributes.php(645): Illuminate\\Validation\\DatabasePresenceVerifier->getCount('users', 'email', 'ehsan.elahi@zer...', NULL, NULL, Array)
#9 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Validation/Concerns/ValidatesAttributes.php(617): Illuminate\\Validation\\Validator->getExistCount(NULL, 'users', 'email', 'ehsan.elahi@zer...', Array)
#10 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Validation/Validator.php(365): Illuminate\\Validation\\Validator->validateExists('email', 'ehsan.elahi@zer...', Array, Object(Phirater\\Domain\\Validation\\CustomValidator))
#11 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Validation/Validator.php(268): Illuminate\\Validation\\Validator->validateAttribute('email', 'Exists')
#12 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Validation/Validator.php(293): Illuminate\\Validation\\Validator->passes()
#13 /home/vagrant/code/phirater-l51/app/Domain/Sessions/LoginValidator.php(27): Illuminate\\Validation\\Validator->fails()
#14 /home/vagrant/code/phirater-l51/app/Domain/Configuration/ValidationCommandBus.php(84): Phirater\\Domain\\Sessions\\LoginValidator->validate(Object(Phirater\\Domain\\Sessions\\LoginCommand))
#15 /home/vagrant/code/phirater-l51/app/Domain/Configuration/ValidationCommandBus.php(62): Phirater\\Domain\\Configuration\\ValidationCommandBus->validateCommand(Object(Phirater\\Domain\\Sessions\\LoginCommand))
#16 /home/vagrant/code/phirater-l51/app/Domain/Core/ValidationCommandBus.php(15): Phirater\\Domain\\Configuration\\ValidationCommandBus->execute(Object(Phirater\\Domain\\Sessions\\LoginCommand))
#17 /home/vagrant/code/phirater-l51/app/Http/Controllers/SessionsController.php(57): Phirater\\Http\\Controllers\\SessionsController->execute(Object(Phirater\\Domain\\Sessions\\LoginCommand))
#18 [internal function]: Phirater\\Http\\Controllers\\SessionsController->auth(Object(Illuminate\\Http\\Request))
#19 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Controller.php(54): call_user_func_array(Array, Array)
#20 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/ControllerDispatcher.php(45): Illuminate\\Routing\\Controller->callAction('auth', Array)
#21 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Route.php(212): Illuminate\\Routing\\ControllerDispatcher->dispatch(Object(Illuminate\\Routing\\Route), Object(Phirater\\Http\\Controllers\\SessionsController), 'auth')
#22 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Route.php(169): Illuminate\\Routing\\Route->runController()
#23 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Router.php(665): Illuminate\\Routing\\Route->run()
#24 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(30): Illuminate\\Routing\\Router->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#25 /home/vagrant/code/phirater-l51/vendor/graham-campbell/throttle/src/Http/Middleware/ThrottleMiddleware.php(64): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#26 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): GrahamCampbell\\Throttle\\Http\\Middleware\\ThrottleMiddleware->handle(Object(Illuminate\\Http\\Request), Object(Closure), '45', '5')
#27 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#28 /home/vagrant/code/phirater-l51/app/Http/Middleware/RedirectIfAuthenticated.php(45): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#29 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): Phirater\\Http\\Middleware\\RedirectIfAuthenticated->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#30 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#31 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(104): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#32 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Router.php(667): Illuminate\\Pipeline\\Pipeline->then(Object(Closure))
#33 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Router.php(642): Illuminate\\Routing\\Router->runRouteWithinStack(Object(Illuminate\\Routing\\Route), Object(Illuminate\\Http\\Request))
#34 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Router.php(608): Illuminate\\Routing\\Router->runRoute(Object(Illuminate\\Http\\Request), Object(Illuminate\\Routing\\Route))
#35 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Router.php(597): Illuminate\\Routing\\Router->dispatchToRoute(Object(Illuminate\\Http\\Request))
#36 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(176): Illuminate\\Routing\\Router->dispatch(Object(Illuminate\\Http\\Request))
#37 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(30): Illuminate\\Foundation\\Http\\Kernel->Illuminate\\Foundation\\Http\\{closure}(Object(Illuminate\\Http\\Request))
#38 /home/vagrant/code/phirater-l51/app/Http/Middleware/SslRedirect.php(22): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#39 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): Phirater\\Http\\Middleware\\SslRedirect->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#40 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#41 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/View/Middleware/ShareErrorsFromSession.php(49): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#42 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): Illuminate\\View\\Middleware\\ShareErrorsFromSession->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#43 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#44 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Session/Middleware/StartSession.php(63): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#45 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): Illuminate\\Session\\Middleware\\StartSession->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#46 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#47 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Cookie/Middleware/AddQueuedCookiesToResponse.php(37): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#48 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): Illuminate\\Cookie\\Middleware\\AddQueuedCookiesToResponse->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#49 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#50 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Cookie/Middleware/EncryptCookies.php(66): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#51 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): Illuminate\\Cookie\\Middleware\\EncryptCookies->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#52 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#53 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/CheckForMaintenanceMode.php(62): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#54 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): Illuminate\\Foundation\\Http\\Middleware\\CheckForMaintenanceMode->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#55 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#56 /home/vagrant/code/phirater-l51/vendor/dingo/api/src/Http/Middleware/Request.php(111): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#57 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(151): Dingo\\Api\\Http\\Middleware\\Request->handle(Object(Illuminate\\Http\\Request), Object(Closure))
#58 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Routing/Pipeline.php(53): Illuminate\\Pipeline\\Pipeline->Illuminate\\Pipeline\\{closure}(Object(Illuminate\\Http\\Request))
#59 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(104): Illuminate\\Routing\\Pipeline->Illuminate\\Routing\\{closure}(Object(Illuminate\\Http\\Request))
#60 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(151): Illuminate\\Pipeline\\Pipeline->then(Object(Closure))
#61 /home/vagrant/code/phirater-l51/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(116): Illuminate\\Foundation\\Http\\Kernel->sendRequestThroughRouter(Object(Illuminate\\Http\\Request))
#62 /home/vagrant/code/phirater-l51/public/index.php(52): Illuminate\\Foundation\\Http\\Kernel->handle(Object(Illuminate\\Http\\Request))
#63 {main}
"} 

This is my LoginValidator class:

class LoginValidator
{
    /**
     * @param $command
     *
     * @throws LoginException
     */
    public function validate($command)
    {
        $validator = \Validator::make(
            [
                'email'    => $command->email,
                'password' => $command->password,
            ],
            [
                'email'    => ['required', 'email', 'exists:users,email'],
                'password' => ['required', 'min:3']
            ],
            [
                'email.exists'    => "Username and password didn't match"
            ]
        );

        if ($validator->fails()) {
            throw (new LoginException())
                ->setErrors($validator->messages());
        }
    }

} 

Apparently the error originates from this line if ($validator->fails()). What is going wrong here? What is the solution?